Page 1 of 3 Form No. 609-02004, Rev. 2June 2019

Tech Manual Excerpt

Basics of Reverse OsmosisMembrane Description

MembraneDescription

The FILMTEC™ membrane is a thin-film composite membrane consisting ofthree layers: a polyester support web, a microporous polysulfone interlayer,and an ultra-thin polyamide barrier layer on the top surface. Each layer istailored to specific requirements. A schematic diagram of the membrane isshown in Figure 1.

Figure 1: Schematic cross-section of a FILMTEC™ thin-film compositemembrane

Polyamide, Microporous Polysulfone, Polyester Support Web, Ultra-thin Barrier Layer0.2 µm, 40 µm, 120 µm

FILMTEC™ produces two different types of polyamide membranes for use inwater purification. The first is the FT30 chemistry, which is an aromaticpolyamide and is used in all FILMTEC™ reverse osmosis membranes and theNF90 nanofiltration membrane patented by John Cadotte at FILMTEC™ in1969.  The second type is a mixed aromatic, aliphatic polyamide used in allnanofiltration membranes and was also initially developed by John Cadotteat FILMTEC™. Thirty years of further innovations at FILMTEC™ have led tothe broadest range of nanofiltration and reverse osmosis membranes in theindustry. FILMTEC™ membranes cover a flux performance range from 0.04– 0.55 gfd/psi (1 – 14 l/m2h bar). This 14-fold difference in water permeabilityis covered by two polyamide types with small changes in composition andlarger changes in the water content of the membrane: the aromatic FT30membrane and the aliphatic/aromatic nanofiltration membrane. The lattertype is sometimes referred to as polypiperazine membrane.

MembraneDescription (Cont.)

Figure 2 represents the approximate structure of the FT30 aromaticpolyamide membrane. The presence of both amine and carboxylate endgroups are shown.

Figure 2: Barrier layer of the FT30 aromatic polyamide membrane

The FT30 membrane is an aromatic polyamide made from 1,3 phenylenediamine and the tri-acid chloride of benzene.  This remarkably chemicallyresistant and structurally strong polymer contains carboxylic acid and free(not reacted) amines at different levels. High chemical stability makes it themost durable and easy to clean membrane material available.

The approximate structure of most of the FILMTEC™ nanofiltrationmembrane is shown in Figure 3. This is an aromatic/aliphatic polyamidewith amine and carboxylate end groups.

Figure 3: Barrier layer of the aromatic/aliphatic polyamide nanofiltrationmembrane

Because of the trace additives and the different dissociation constants ofthe piperazine found in this polymer we are able to have a wider range ofboth monovalent and divalent salts transporting through this polymer. Thishas allowed us to design a wide range of nanofiltration membranes thathave different salt selectivity for different separations.

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MembraneDescription (Cont.)

The major structural support is provided by the non-woven web, which hasbeen calendered to produce a hard, smooth surface free of loose fibers.Since the polyester web is too irregular and porous to provide a propersubstrate for the salt barrier layer, a microporous layer of engineeringplastic (polysulfone) is cast onto the surface of the web.

The polysulfone coating is remarkable in that it has surface pores controlledto a diameter of approximately 150 Angstroms. The barrier layer, about2,000 Angstroms thick, can withstand high pressures because of the supportprovided by the polysulfone layer. The combination of the polyester weband the polysulfone layer has been optimized for high water permeability athigh pressure.

The barrier layer is relatively thick; making FILMTEC™ membranes highlyresistant to mechanical stresses and chemical degradation.

Excerpt from FILMTEC™ Reverse OsmosisMembranes Technical Manual, Chapter 1, "Basics of Reverse Osmosis and Nanofiltration."

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